The invention relates to a separation column for liquid chromatography. Generally, separation columns for liquid chromatography, in particular those having relatively small diameters, are closed tightly with frits after packing for the purpose of reducing the remaining dead volume as much as possible. In chromatographic separation columns having relatively large diameters, however, it has previously not been possible to pack then in such a way that a packing of completely constant volume results. Instead, when eluent is pumped through, the packing is compressed, as a rule, by about 0.5-2% of the column length, depending on the type of packing material and the method of packing.
In addition, a shrinkage of the packing occurs indendently of the column dimensions. More particularly, this shrinkage especially occurs when polar solvents are used due to the solubility of the sorbents in the eluent; said solubility, although small, is nevertheless significant in continuous operation. In columns which are closed tightly by frits on both sides at the end faces, all these effects lead to an increase in the dead volume between the packing and the frit, resulting in a decrease of the separation efficiency of the column. In addition, the increase in dead volume combined with the drying out of the column, which is not avoidable in practice, combines with shocks and formation of cracks to result in the total destruction of the packing.
Proposals have been made in the past to avoid the dead volume by closing the end of the column by means of stoppers capable of being positioned at adjustable heights. Nonetheless, in the case of columns having relatively large diameters, sealing of the stoppers at the periphery of the column raises problems, since the tolerance in diameter variations are required to be very small. Furthermore, whenever columns of glass, and stoppers having polytetrafluoroethylene gaskets are required because of their good resistance to chemicals, this proposal is not feasible in practice because of the risk of fracture.
German Offenlegungsschrift No. 2,655,650 discloses columns in which a dead volume in the column packing is prevented by radial compression of the column. To achieve this, however, the column itself must consist of an elastic material. Therefore, this proposal cannot be applied to conventional columns of metal, glass or a pressure-resistant plastic.